Forrester was educated in electrical engineering at the University of Nebraska, Lincoln, and the Massachusetts Institute of Technology (MIT), Cambridge, where he remained to teach and do research. In 1945 he founded the Digital Computer Laboratory there and participated in the construction of Whirlwind I, an early general-purpose digital computer designed for the U.S. Navy. During the course of this work, he realized that the slow and unreliable information-storage systems of early digital computers hindered their further development. In 1949 Forrester devised in 1949 a memory system that stored information in three dimensions; in his invention a magnetic cell was employed for both storage and switching.

From 1951 until 1956, Forrester was associated with the Lincoln Laboratory, operated by MIT in Lexington, Mass., operated by MIT for the federal government to apply electronic technology to problems of the national defense. In particular, Forrester, together with his Lincoln Laboratory colleague George Valley, came up with the plan for the U.S. Air Force’s Semi-Automatic Ground Environment (SAGE) air defense computer system, which was developed from the Whirlwind prototype in cooperation with International Business Machines Corporation (IBM), Burroughs Corporation (later merged into the Unisys Corporation), Western Electric Company, Inc., and other subcontractors. SAGE included 23 Direction Centers in the United States and 1 in Canada, with each of these radar and missile installations being controlled by its own computer, though all the computers were in continual contact with each other for data exchange and analysis. Partially operational by 1958 and fully operational in 1963, SAGE was the brains behind the American air defense system into the 1980s.

Forrester was led to experiment with the application of computers to management problems. In time he devised the technique of computer simulation in which real-world relationships, such as the flow of materials in a factory, are represented as a series of interconnected mathematical equations that can be fed to the computer. He is thus often credited as being the father of systems dynamics, essentially the application of techniques used in systems engineering to nonengineering problems. As a professor in MIT’s Sloan School of Management, from 1956, Forrester wrote several books about systems dynamics, including Industrial Dynamics (1961), Principles of Systems (1968), Urban Dynamics (1969), and World Dynamics (1971). His Collected Papers appeared in 1975.

In 1982 Forrester was honoured by the Institute of Electrical and Electronics Engineers (IEEE) as a Computer Pioneer Charter Recipient. He was awarded the U.S. National Medal of Technology in 1989, the year that he retired.